Ultrabandwidth miniature resonance absorption isolator



June 25, 1962 vULTRABNDWIDTH MINIATURE RsowmcE ABSORPTIQN ISOLATOR Filed Deo. 51, 1956 Magnetic Fie Intensity Gaussbistance across waveguide 14 n X .S5- ,Y /k 4 a/. Jb, cf b'. rf /l wifi, alla s,

,m /T gl D/ ls A g I n 71A-,

rw 9 4 s -L l p wld A Y P, \P P a aymon oung, '.2 's Lawrence A.Blasberg, Fig. 3. /NVE/vroRs.

E ma..

AGENT.

States The present invention relates in general to isolator devices used in waveguide systems and more particularly to a relatively small, light-weight, and ultra broad band ferromagnetic resonance absorption type of isolator having a relatively small voltage-standing-wave ratio and insertion loss over the operating bandwidth.

As is generally known, isolators are used to provide load independent impedances to microwave sources. This is often desirable since the output power, frequency and frequency stabilityof microwave generators are functions of the impedance into which the generator works. Thus, the basic function of an isolator is -to make the characteristics of a microwave generator independent of the load.

y, There are several different species of isolators which may be classified according to the non-reciprocal property utilized. `For example, rotation and phase shift isolators utilize the non-reciprocal phase constant of a ferrite loaded waveguide, field displacement isolators utilize the non-reciprocal eld configurations of ferrite loaded waveguide, and resonance `absorption isolators utilize nonreciprocal attenuation of ferrite loaded waveguide. The isolator device of the present invention is of the last type.

'It was the practice at one time to provide a resonance absorption isolator by disposing a ferrite slab parallel to and lalong the longitudinal axis of a rectangular waveguide between the "broad sides thereof lat a point approximately one-quarter of the width of the waveguide from one side. A uniform magnetic eld was then produced through the ferrite slab in a direction transverse to the longitudinal axis of the waveguide. The intensity of this magnetic eld together with the characteristics of the ferrite material constituting the slab determined the frequency at which unidirectional attenuation occurred. In this type of isolator, however, it was only possible to achieve a 4back-to-front power absorption ratio of lapproximately twenty-five to one decibels.

The poor performance of an isolator of this type may be attributed to the serious distortions of the electric and magnetic elds of the wave being propagated caused by the introduction of even a very thin ferrite slab in the waveguide. In addition, within the region of the ferrite slab, there is no pure negative circular polarization of the propagated wave in the unattenuated direction. Also, since only the edges of the ferrite slab are in contact with the metallic walls of the waveguide, there is very poor heat dissipation from the slab.

These difficulties encountered in the early prior art were solved by means of a new and improved resonance absorption isolator which is disclosed in copending U.S. patent application, Serial No. 572,176 by Lawrence A. Blasberg, Leon I. Lader and Raymond A. Young for A High-Power Resonance Absorption Isolator, tiled March l5, 1956, now abandoned. According to the embodimentof the invention shown and described in this copending application, at least one ferrite slab is disposed contiguous to the inner surface of the broad side of a section of rectangular waveguide with at least a portion of the slab located in the region midway between the center line and one edge of a broad side. If desired a second ferrite slab may be disposed opposite the iirst ferrite slab contiguous to the opposite broad side.

Aarent O A direct-current magnetic eld is produced across the narrow dimension of the waveguide through the thickness of the ferrite slab, the intensity of this magnetic eld varying asymmetrically in such la manner that in proceeding through the ferrite slab in the region between the center line and one edge of the broad side, the value of intensity equals that which is required to produce gyroresonance effects within the ferrite material at the frequency of the electromagnetic wave propagated through the waveguide.

Considering its operation, the polarity of the directcurrent magnetic eld is oriented so that energy reflected from a load impedance precesses the magnetic dipoles within the ferrite slab in the region where a magnetic field is of an intensity to produce gym-resonance. As a result, a certain amount of reflected energy is absorbed per unit volume of ferrite material. Attenuation is euhanced in that the precessing dipoles coupled to the re` ilected wave in turn couple to the remaining dipoles within the ferrite slab.

Although the isolator disclosed in the `aforementioned copending application represents a marked improvement over earlier isolators, it nevertheless has certain undesirable features about it which restrict its applicability. Thus, for example, the ability of the isolator to isolate theiload from the microwave source, that is, the ability of the isolator to absorb reflected energy is very much determined by the thickness of the ferrite material placed inside the isolator waveguide, the thicker the ferrite slab the more effective the isolation. On the other hand, however, the insertion of ferrite slabs introduces a mismatch which causes an linsertion loss. The extent of the mismatch is also related to the thickness `of the ferrite material, the thicker the ferrite material the greater the mismatch and, therefore, the greater the insertion loss. It is thus seen that isolation that is made to depend upon thethickness of the ferrite slab is incompatable with the achievement of a good match and consequently, incompatable with optimum power transfer.

The difficulty just mentioned was resolved in some instances by inserting relatively thin ferrite slabs but of much greater length than that required of thick slabs, thereby greatly reducing the mismatch as well as the insertion loss due to the mismatch while at the same time achieving the desired high degree of isolation. However, along with the thinner and longer ferrite slabs, a longer isolator waveguide section had to be used as well as a larger magnet to provide the required magnetic field, thereby very greatly increasing the bulk, weight and eX- pense of the nal isolator product.

A resonance absorption isolator having a good impedance match and relatively low insertion loss is shown and described in copending U.S. patent application, Serial No. 594,162 :by Lawrence A. Blasberg and Raymond A. Young for A Resonance Absorption Isolator, led lune 27, 1956, now abandoned. As explained therein, `arl isolator having these beneficial qualities may be obtained by purposely introducing a mismatch that nullies or vitiates any mismatch caused by the ferrite slabs placed in the isolator waveguide. More particularly, the narrow sides of the isolator waveguide are made smaller than the corresponding sides of the standard waveguide to which the former is coupled. This dilference in waveguide dimensions, that is, this step in going from the standard waveguide to the isolator waveguide is equivalent in eifect to introducing a quarter-wavelength impedance transformer between the standard waveguide and the ferrite slabs of the isolator waveguide. Thus, by employing such a novel technique, the input impedance of the isolator waveguide vat the ferrite slabs is matched to the characteristic impedance of the standard waveguide used in the microwave network, thereby greatly reducing the insertion loss of the isolator.

Because the mismatch caused by the ferrite slabs can be substantially eliminated, it becomes feasible, therefore, to use relatively thick slabs of ferrite material to h1ghly attenuate energy reflected from the microwave load. As a result, the length of the ferrite slabs may be considerably shortened while at the same time achieving, for the reasons previously presented, thedesired high degree of isolation between the load and the generator. It will be obvious that since Vshorter slabs may be used, a correspondingly smaller waveguide section and magnet are required. Furthermore, the use of relatively thick slabs reduces the air gap and, consequently, the reluctance between the slabs. Thus, the magnetomotive force required to produce the desired flux distribution is correspondingly reduced and the magnet can be further reduced in size. Also, the isolator of this last copending application has less bulk and weight and can be made more cheaply than the earlier types of isolators. However, although this mosty recent isolator invented by Blasberg and Young represents a most significant advance in the art, Ythe isolator nevertheless has limitations associated with it which restrict its usefulness.

Specilically, the isolator of copending U.S. patent application, Serial No. 594,162 by Blasberg and Young has alimited bandwidth, namely, a ten percent bandwidth, the voltage-standing-wave ratio outside this ten percent frequency band being greater than 1.2. This means that outside the ten percent bandwidth, the high VSWR would pull microwave cavities and generators, thereby vitiating their perfomance. The insertion loss will Valso signicantly increase which, in turn, means an increased loss of power. Accordingly, asis often the case, although the Blasberg and Young isolator has represented a step forward'in the art and has proven to be highly successful, it nevertheless could Vbe further improved to extend the scope of its utility.v

It'is therefore an object of the present invention to provide a resonance absorption/isolator having a relatively low insertion loss over a wide bandwidth of operation.

It is another object of the present invention to provide a resonance absorption Visolator that is substantially matched to the rest of the waveguide system.

" It`is'a further object of the present invention to provide a resonance absorption isolator wherein relatively thick slabs of ferrite material maybe used to provide a high degree Vof isolation without, at the same time, causing 'any 'substantial insertion loss.

ItV is still another object of the present invention to provide a'resonance absorption isolator wherein any mismatch introduced by theuse of ferrite slabs is substantially nullified by the deliberate introduction of additional mismatches which match out the first mismatch.

' It is 'an' additional object of the present invention to provide a resonance absorption isolator of relatively small bulk and weight. I A Y Y l It is still a further object of the present invention to provide a resonance absorption isolator of relatively small b ulk andfweight that has, nevertheless, high power handlin'g capacity.

It is another and further object of the present invention to provide la resonance absorption isolator having a relatively low voltage-standing-wave ratio over an eX- ceptionally wide band of operation.

A highly improved resonance absorption isolator having a good impedance match and a relatively low insertion loss over an ultra wide band of frequencies is the subject-matter of the present invention and can be made by purposely introducing several mismatchesV or discon-A tinuities which nullify or vitiate any mismatch caused by Ythe ferrite slabs .and also extend the desirable operating range of the isolator. More particularly, at each end of the isolator'waveguide section, the height dimensions of the narrow sides of the waveguide section are successively reduced so that, in going from a standard waveguide that may be coupled to the isolator to the ferrite slabs in the isolator, one encounters several discontinuities or steps.

In the present invention, two discontinuities have been provided between the ferrite slabs and the standard waveguide coupled to each end of the isolator, each set of two discontinuities acting as a double quarter-wavelength matching transformer. It is by means of this equivalent double quarter-wavelength transformer that the input impedance of the isolator waveguide is matched to the characteristic impedance of the standard waveguide over an extremely wide band of frequencies, thereby greatly reducing the voltage-standing-wave ratio and insertion loss over the same ultrabandwidth.

It should be noted that here as in the isolator previously invented by Blasberg and Young, see the reference above to copending U.S. patent application, Serial No. 594,162, since the mismatch caused by the ferrite slabs can be substantially eliminated, itV becomes feasible to use relatively thick slabs of ferrite material which makes it possible to obtain a relatively high degree of attenuation or isolation over the previously mentioned wide band of operation. Consequently, the length of the ferrite slabs may be considerably shortened so that a correspondingly smaller waveguide section and magnet are required. Furthermore, as before, the use of relatively thick slabs reduces the air gap and, consequently, the reluctance between the slabs. Also, the magnetomotive force required to produce the desired flux distribution is Vcorrespondingly reduced and the magnet can be further reduced in size. v Thus, the isolator of the present invention also has comparatively little bulk and weight and can be; made more'cheaply than similar types of isolators to be found in the prior art.

From what has been said above, it will be obvious that the isolator of the present invention not only has all the advantages of the isolator previously invented by Blasberg and Young but also has the additional advantage of being operable with low voltage-standing-wave ratio and low insertion loss over an extremely Wide range of frequencies.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that Vthe drawing is for the purpose of illustration and description only, and is not intended as a denition of the limits of the invention.

FIG. l is a schematic perspective view of an embodiment of the isolator of the present invention;

FIG. 2 is a cross-sectional schematic view of the isolator taken along the 'line 2 2 in FIG. 1;

FIG. 3 is la cross-sectional schematic view of the isolator taken along the line 3 3 in FIG. l; and

FIG, 4 illustrates the magnetic iield distribution in a plane transversely across the isolator waveguide.

Referring now to the drawings, there is shown in FIGS. 1, 2 and 3 a relatively small and lightweight resonance absorption isolator that can provide a high degree of isolation between a microwave lload and generator with aV relatively small voltage-standing-wave ratio and insertion lossrover an ultra wide band of frequencies. Re- -ferring in particular to FIG. 1, the isolator, generally designated 10, comprises a section of rectangular wave- 'guide 11 partly inveloped by a magnet 12 and having flanges 13 and 14 at the ends thereof to enable it to be connected between standard waveguide sections 15 and 16 interconnecting the microwave generator and load. Stand.- ard waveguide section 15 is shown in cross-section for purposes of 4clarity and, furthermore, since the microwave generator and load are not essentialV to any understanding of the invention, they are not shown.

As shown to some extent in FIG. 1 and more clearly shown in FIG. 3, the hollow of waveguide section 11 has several predetermined discontinuities or steps a, b, c and a', b', c' at predetermined points p1, p2, p3 and p1', p2', p3' between the input and output ends of the waveguide section and its middle. More particularly, intermediate the middle of the waveguide section and each of its ends, the inner lheight of the narrow sides of waveguide section 11 is less than the inner height of the narrow sides of standard waveguide sections 15 and 16, the differences in height occurring in three steps and being predetermined. The first points p1 and p1 at which discontinuities or steps occur are at the input and output ends of waveguide section 1.1, Ithe second points p2 and p2 at which discontinuities or steps occur are approximately one-quarter of the waveguide wavelength of the propagated energy from rst points p1 and p1', respectively, and the third points p3 and p3' at which discontinuities or steps occur are approximately one-half of the waveguide wavelength of the propagated energy from first points p1 and p1', respectively.

The extent or amount of the discontinuity or difference in height at each point mentioned above or, stated differently, the inside height of the narrow sides of waveguide section 11, is very closely related to the dimensions of slabs of ferrite material placed in the hollow of the waveguide section. Accordingly, further discussion of these discontinuities and a presentation of mathematical equations tying-in the discontinuities with the -ferrite sl-abs will be postponed until after the referred-to ferrite slabs have been described.

Referring now to FIG. 2, there is shown a pair of ferrite slabs 17 and 18 disposed contiguous to opposite inner surfaces of the respective broad sides of isolator waveguide section 11, the slabs primarily being positioned on one side ,of the waveguide but preferably overlying the centers of the broad sides. Any ferrite material that can be made to exhibit gym-resonance throughout the band of frequencies within which operation is intended may be employed for slabs 17 and 18. As a practical matter, however, it is desirable to employ ferrite materials which have lhigh resistivities so as to minimize insertion loss in the wave propagated in the forward direction due to resistance losses. Examples of ferrite materials which have been -found to be suitable for slabs 17 and 18 are ferrites known commercially as General Ceramic R-l.

The width, thickness and length of the ferrite slabs are not irrevocably xed but are, rather, primarily determined by the design of the isolator, that is, by the electrical properties it is desired -to impart to the isolator, such as the amount of isolation per unit length. By way of example, in one isolator designed for X-band operation, the Width, thickness and length of ferrite slabs 17 and 13 are 400 mils, 65 mils and 1.62 inches, respectively.

As previously mentioned, the extent of the discontinuities are very closely related to the dimensions, more specilically, the thickness, of the ferrite slabs placed in the hollow of waveguide section l1. This relationship between the discontinuities or, stated differently, the various heights of the isolator waveguide section and the thickness of the ferrite slabs as well as the height of standard waveguide sections 15 and .16 is set out in the following mathematical equations, namely,

wherein, b1 is the actual inner height of standard waveguide sections 15 and 16; b2 is the actual inner height of isolator waveguide section 11 between first and second points p1 and p2 and p1 and pz; b3 is the actual inner height of isolator waveguide section 11 between second and third points p2 and p3 and p2' and p3; and b4 equi is the equivalent inner height of isolator waveguide section 11 between third points p3 and p3. The relationship between the equivalent height b4 equiv, of the ferrite loaded portion of the waveguide section, the actual waveguide height thereat, and the ferrite dimensions may be set out rin two mathematical equations as follows:

bftequimgblinztequlv.

where, t is the `actual thickness of a ferrite slab; tequiw is the equivalent thickness of a ferrite slab and is the individual thickness of two pieces of metal covering the entire top and bottom width of the ferrite loaded portion of the isolator waveguidel section that produce the same impedance effect as the two ferrite slabs; k is the dielectric constant of the ferrite material; x is the distance of a point inside the isolator waveguide section from a narrow side of the waveguide section used as a reference; x1 is the distance of one side of the ferrite slabs from the reference side; x2 is the distance of the other side of the ferrite slabs from the reference side; a is the width of the broadsides of the standard land isolator waveguide sections; and b4 is the actual inner height of isolator waveguide section 11 between third points p3 and p3.

In using Equations 1 through 4 to design an ultrabandwidth isolator, a particular waveguideheight b4 is chosen, preferably one that will conserve magnet, and a particular thickness t of Yferrite material to give the desired isolation per unit volume. Equations l, 2, 3, and 4 then determine waveguide heights b2 land b3, the length of isolator waveguide at each height being 14mg. As previously mentioned, this technique enables one to design an extremely broad band isolator, 30% bandwidth, with low voltage-standing-Iwave ratio, low insertion loss and high isolation.

In addition to ferrite slabs 17 and 18, the apparatus vfor producing the asymmetrical magnetic field distribution across waveguide section 11 includes magnet 12, which may be either a permanent magnet or an electromagnet, and a pair of pole pieces 20 and Z1. The pole pieces preferably extend for the entire length Vof waveguide section between points p3 and p3 and are inserted through apertures in the waveguide section that are disposed directly opposite each other in the broad sides thereof and oriented so Vas to be parallel to the longitudinal axis of the waveguide section. The apertures are preferably 0.150 inch wide and are disposed along the broad sides of waveguide section 11 over the edges of ferrite slabs 17 and 18 nearest the side of the waveguide, Ias shown in FIG. 2. The face of each pole piece is made fllush with the inner surface of the yassociated broad side of waveguide section 11. Moreover, pole pieces 20y and Z1 are preferably made of 0.150 inch thiok Armco iron so as to completely fill the apertures, only about 0.100 inch of the face of each pole piece being covered by the corresponding ferrite slab.

Magnet 12 is of the horseshoe type and may, for example, be composed of a magnetic material known commercially as Alnico V. In order to achieve the magnetic flux distribution in accordance with the present invention, magnet 12 is disposed over the portion of waveguide section 11 including the center lines of the broad sides thereof so that the pole faces of the magnet are contiguous to pole pieces 17 and 18, as shown in FIG. 2. The magnetic eld distribution thus produced is represented by characteristic 22 in FIG. 4. Referring to FIG. 4, a partial cross section of the device Vof FIG. 1 including ferrite slab 18, pole piece 21, and a portion of waveguide section 11 is shown for the purpose of 7VV referencing magnetic field intensity versus position across the waveguide. 1 Y i In accordance with the present invention, the magnetic field intensity as represented by characteristic 22 must pass through or equal that intensity required to bring about gyro-resonance within ferrite slabs 17 and 18 along a region therein where there issubstantially pure circular polarization. In the present case, a region of this type is located midway between the centerlines and the respective edges of the broad sides of the waveguide. In the event that the ferrite slabs arecomposed of General Ceramic R-l ferrite material, the magnetic field intensity to elect gym-resonance in the X-band region is of the order of 4,000 gauss. Also, in proceeding toward a centerline from the nearest point thereto at which gyroresonance in the ferrite material is effected, the magnetic iield intensity progressively decreases until the intensity at the centerline is substantially less than that required to produce gyro-resonance. Furthermore, in the event that the ferrite slabs should extend across the centerlines, the intensity of the magnetic field in the plane between the centerlines is made less than that required to produce gyro-resonance so as not to elect bidirectional attenuation.

Considering now the operation, electromagnetic energy in the form of a TEN, mode is propagated in a forward direction, that is, toward the load, through Waveguide section 1S, waveguide section 1l of isolator 10, and waveguide sectionl, as indicated byV arrow 23. As is generally known, when electromagnetic energy is propagated in the TEN mode, the magnetic` eldwis circularly polarized positively or clockwise at Vsome point on one side of the waveguide with respect to Van applied transverse static magnetic field whereas on the other side of the waveguide, the magnetic iield is circularly polarized negatively or counter-clockwise with respect. tofthat applied field. Y

This relationship with respect `to the applied field. is reversed for propagation in thereverse direction. AThus, when energy is reflected from the load and is propagated toward the microwave generator, YtheV radio-frequency magnetic field of the reflected energy is cireularly polarized oppositely to that of the incident energy, More specilically, the magnetic eld of the reflected energy is circularly polarized counter-clockwise ,and Yclockwise on the'sides of the waveguide whereat the magnetic eld of the forwardly propagated energy is circularly polarized clockwise and counter-clockwise, respectively.

-In accordance with the present invention, `the polarity of the direct-current magnetic field produced kby magnet 12 is poled so as to couple to the circularly polarized magnetic eld of the reflectedY energy. InV this way,ethe reflected energy is almost entirely absorbed bythe `ferrite slabs and dissipated in the form ofheat through the Wallis of the isolator waveguide.

Reference is now made to the reason for the discon-V tinuities purposely introduced at'vpoints p1, p2, p3Y andV p1', p2', p3'. Since point p3 is one-half wavelength away from point 171, the total distance'from point p1 to point p3 and back again to to point pl is Vone wavelength. Thus, reections from the discontinuity at point p3, that is, from ferrite slabs 17 and 18, will'be in phase with reflections from the discontinuity at point p1'. Consequently, the reflections from points p1 and p3 will add. On the other hand, since the round-trip distancefrom point p1 to p2 is one-half wavelength, Yreflections reaching point p1 from point p2 are 180 out of phase with thereilections from points p1 and p3. Furthermore, since the discontinuity or step at pointpz is twice las great as at either points lp1 or p3, as previously mentioned, the re- -ections from point p2 are not only of opposite polarity but also equal in magnitude to the sum of the reflections from points p1V and point p3. Asjaresult, the reflected energy from point p2 cancels the reile'cted energy from points p1 and p3.

Thus, the mismatch introduced by the ferrite slabs, which mismatch also varies directly as the width and thickness of the ferrite material, is substantially eliminated. It will be obvious, therefore, that the present invention makes it possible to practically eliminate reflections and insertion loss from the isolator and at the same time achieve a high degree of isolation with the use of relatively wide and thick but relatively short slabs of ferrite material. Moreover, the several discontinuities are equivalcnt to introducing a double quarter-wavelength matching transformer'between isolator 16 and standard waveguide 15. It will be obvious therefore, that the broad band characteristics of a double-quarter wavelength matching transformer will be introduced into the waveguide network so that mismatches caused by the ferrite slabs may be very greatly reduced over an extremely wide range of frequencies, thereby greatly reducing the voltagestanding wave ratio and insertion loss over the same range.

By way of example, the following table presents the perform-ance characteristics of an ultrabandwidth resonance absorption isolator for different bandwidths-in the X-band region of operation. The ferrite slabs are 2.3 inches long and the weight of the Alnico magnet is 8.8 ounces.

Fre-

quency Forward Reverse Insertion, Isolation,

Band- VSWR VSWR Loss, db db width,

Percent l0 1.03 l. 03 0. 5 60-100 20 l. l0 1. l0 0.6 50-100 30 1. 25 1. 25 O. 7 t0-100 interior dimension associated with each step, the narrow interior dimension of the stepped portion immediately adjacent said center portion being smaller by a predetermined amount than said first predetermined narrow interior dimension, the narrow interior dimensions of additional steps increasing progressively by predetermined amounts with distance fromV said center portion; a pair of ferrite slabs having a thickness which is greater than the step between the center portion and immediately adjacent narrower portion, the thickness of said slab being related to said rst predetermined narrow interior dimension, said slabs being positioned inside said center portion and longitudinally disposed contiguous to the inner surface of the broad walls of said center portion between the longitudinal center line and one side thereof; and magnetic field means associated with said ferrite slabs for establishing a magnetic field transversely to broad walls of said waveguide through said ferrite slabs.

2. An electromagnetic wave transmission device for isolating a microwave generator from a load, said device comprising: a waveguide of rectangular cross-section having a center portion and stepped end portions on either end of said center portion, said center portion having a lirst predetermined narrow interior dimension, each of said stepped end portions including at least two symmetrically opposed steps, the longitudinal length of each of said steps being approximately one-quarter of a waveguide wavelength, a narrow interior'dirnension associated with each step, the narrow interior dimension of the stepped portion immediately adjacent said center portion being smaller by a predetermined amount than said Erst predetermined narrow interior dimension, the narrow interior dimensions of successive steps progressively and stepwise increasing by predetermined amounts with quarter waveguide wavelength distance from said center portion; a pair of ferrites of predetermined thickness each being thicker than the adjacent step dimension and having at least one flat side disposed opposite each other within said center portion immediate the center line and one edge of the broad sides thereof, said at side being contiguous to the inner surface of said center portion; and means for producing a magnetic field transversely through said pair of ferrites, said magnetic eld being of different intensities to eifect gyro-resonance in said ferrites throughout a band of frequencies which include the frequency of electromagnetic energy from said microwave generator and of a polarity to effect coupling between the magnetic dipoles within said pair of ferrites and the portion of the energy generated by said microwave generator that is reflected from said load.

3. An electromagnetic wave transmission device for b1 b2: b1 )1/2 b4equv.

and the width,

b2 bs: b1 )1/4 b4equiv.

b4-2t equiv. and b., is the narrow interior dimension of said center portion greater than b3, each of said two steps having a longitudinal length of one-quarter of the waveguide wavelength; a pair of ferrite slabs each having a thickness t and at least one flat side disposed opposite each other within said center section immediate the center line and one edge of the broad Walls thereof, said at side being contiguous to the inner surface of said center section, the thickness t being -related to the quantity tequi by the expression where x is the transverse distance parallel to said broad walls from a point inside said waveguide, x1 and x2 being respectively the distance from said point to the two sides of each of said ferrite slabs respectively, k being the dielectric constant of said ferrite slabs and a being the broad interior dimension of said waveguide; and means for producing a magnetic eld transversely through said pair of ferrites, said magnetic field being of different intensities to effect gyro-resonance in said -ferrites throughout a band of frequencies which include the frequency of electromagnetic energy from said microwave generator and of a polarity to efect coupling between the magnetic dipoles within said pair of ferrites and the portion of the energy that is generated by said microwave generator that is reflected from said load.

References Cited in the le of this patent UNITED STATES PATENTS 2,531,437 Johnson et al Nov. 28, 1950 2,745,069 Hewitt May 8, 1956 2,767,380 Zobel Oct. 16, 1956 2,776,412 Sparling Ian. 1, 1957 2,806,972 Sensiper Sept. 17, 1957 OTHER REFERENCES Sensiper and Hogan: Proceedings of the IRE, October 1956, pages 1325 and 1365 respectively.

Fox et al.: Bell System Technical Journal, January 1955, pages 5-103 (page 22 relied on). 

